Macrocycles are an important therapeutic class of antibiotics. These compounds are frequently produced as a family of closely related biogenetic congeners. The Tiacumicins are a series of 18-membered macrocyclic antibiotics in which the macrocyclic ring is glycosidically attached to one or two sugars. As shown in Table 1, a seven-carbon sugar (R1) is esterified at various positions with small fatty acids. The other sugar (R2), when present, is esterified with an isomer of substituted benzoic acid such as everninic acid (Journal of Liquid Chromatography, 1988, 11: 191-201).
Tiacumicins are a family of related compounds that contain the 18-membered ring shown in Formula I below.

At present, several distinct Tiacumicins have been identified and six of these (Tiacumicin A-F) are defined by their particular pattern of substituents R1, R2, and R3 (See, e.g., U.S. Pat. No. 4,918,174; J. Antibiotics, 1987, 40: 575-588), as shown in Table 1.
TABLE 1Substituents Present In Tiacumcins A-FR1R2R3AHH BOH COH DOH EOH FOH
More recently, a group of related substances were discovered and described in the U.S. patent application publication number US2007-105791 and include the following.

Tiacumicins can be produced by bacteria, including Dactylosporangium aurantiacum subspecies hamdenensis, which may be obtained from the ARS Patent Collection of the Northern Regional Research Center, United States Department of Agriculture, 1815 North University Street, Peoria, Ill. 61604, accession number NRRL 18085. The characteristics of strain AB 718C-41 are given in J. Antibiotics, 1987, 40: 567-574 and U.S. Pat. No. 4,918,174.
Tiacumicins show activity against a variety of bacterial pathogens and in particular against C. difficile, a Gram-positive bacterium (Antimicrob. Agents Chemother. 1991, 1108-1111). C. difficile is an anaerobic spore-forming bacterium that causes an infection of the bowel. Diarrhea is the most common symptom but abdominal pain and fever may also occur. C. difficile is a major causative agent of colitis (i.e., inflammation of the colon) and diarrhea that may occur following antibiotic intake. This bacterium is primarily acquired in hospitals and chronic care facilities. Because Tiacumicin B shows promising activity against C. difficile, it is expected to be useful in the treatment of bacterial infections, especially those of the gastrointestinal tract, in mammals. Examples of such treatments include but are not limited to treatment of colitis and treatment of irritable bowel syndrome. Tiacumicins may also find use for the treatment of gastrointestinal cancers.
Tiacumicin antibiotics are described in U.S. Pat. No. 4,918,174 (issued Apr. 17, 1990), J. Antibiotics, 1987, 40: 575-588, J. Antibiotics, 1987, 40: 567-574, J. Liquid Chromatography, 1988, 11: 191-201, Antimicrobial Agents and Chemotherapy 1991, 35: 1108-1111, U.S. Pat. No. 5,583,115 (issued Dec. 10, 1996), and U.S. Pat. No. 5,767,096 (issued Jun. 16, 1998), which are all incorporated herein by reference. Related compounds are the Lipiarmycin antibiotics (c.f., J. Chem. Soc. Perkin Trans. I, 1987, 1353-1359 and J. Antibiotics 1988, 41: 308-315) and the Clostomicin antibiotics (J. Antibiotics 1986, 39: 1407-1412), which are all incorporated herein by reference.